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220-1201 Practice Question: A customer reports that their new VoIP phone…
A customer reports that their new VoIP phone cannot register with the company's call server, but their computer on the same switch port works fine. The network uses VLANs for voice and data traffic. Which protocol must be configured on the switch port to separate the voice traffic from the data traffic?
⚠ Common exam trap
The CompTIA A+ exam often tests the distinction between protocols that manage traffic (like DHCP) and protocols that separate traffic (like 802.1Q), leading candidates to mistakenly choose DHCP because it is commonly associated with VoIP phone configuration.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
802.1Q
802.1Q is the IEEE standard for VLAN tagging, which allows a single switch port to carry traffic for multiple VLANs. In this scenario, the switch port must be configured as an 802.1Q trunk or use a voice VLAN feature that tags VoIP traffic with a specific VLAN ID, separating it from the untagged data traffic. This ensures the VoIP phone can communicate with the call server on its designated voice VLAN while the computer continues to work on the data VLAN.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
DHCP
Why it's wrong here
DHCP (Dynamic Host Configuration Protocol) is responsible for automatically assigning IP addresses, subnet masks, default gateways, and DNS server information to network devices. While a DHCP server can be configured to provide different IP address ranges based on VLANs, it does not perform the actual Layer 2 process of tagging Ethernet frames or separating traffic into distinct VLANs. Its function is at the network layer (Layer 3) to configure host IP settings, not to manage VLAN membership or frame identification.
- ✓
802.1Q
Why this is correct
802.1Q is the IEEE standard for Virtual Local Area Networks (VLANs) that defines how to insert a 4-byte tag into an Ethernet frame header. This tag contains a VLAN ID, allowing a single physical network interface or switch port to carry traffic for multiple logical VLANs. For a VoIP phone, 802.1Q tagging is essential for segregating voice traffic into a dedicated VLAN, often with Quality of Service (QoS) priority, from general data traffic on the same physical cable, ensuring proper call quality and network segmentation.
- ✗
DNS
Why it's wrong here
DNS (Domain Name System) is an application layer protocol used to translate human-readable domain names (e.g., example.com) into numerical IP addresses that computers use to identify each other on a network. Its primary function is name resolution, enabling users to access network resources without needing to remember complex IP addresses. DNS has no direct involvement in the Layer 2 process of segmenting network traffic into VLANs or tagging Ethernet frames for VLAN identification.
- ✗
ARP
Why it's wrong here
ARP (Address Resolution Protocol) is a communication protocol used to discover the link layer address (MAC address) associated with a given internet layer address (IP address) on the same local network segment. When a device needs to send data to another device on the same local network and only knows its IP address, it uses ARP to find the corresponding MAC address. ARP operates at Layer 2 and Layer 3, but its function is address resolution within a broadcast domain, not the creation or management of VLANs or the tagging of frames for VLAN identification.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1201 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1201 exam.